1. Field of the Invention
The present invention relates generally to asset tracking. More specifically, the present invention pertains to determining the location of objects in a distributed communications network.
2. Related Art
The development of an efficient lightweight protocol to determine the topology of a wireless network of mobile hosts has proven to be elusive. Several conventional solutions have been explored, but each has serious limitations. Table 1 below provides a summary of these conventional approaches.
TABLE 1Positioning TechnologiesMethodAdvantagesDisadvantagesRangeGPSCovert;Not a sensor;Range: UnlimitedAbsolute Position;Coverage area;Accuracy: metersAccurate timingPower ConsumptionHardware: LotsreferenceINSCovert;Not a sensor;Range: Unlimited;Absolute PositionLimitedAccuracy: n/aAcceleration;Hardware: LotsDrift rate inaccuracywith timeSeismicExisting Sensor;Generating theRange: Limited(range)Timing accuracysource signal;Accuracy: meterseasily achieved;Unknown speed ofHardware: SourceCalibration of thepropagationgeneratorsensorAcousticExisting Sensor;Not Covert;Range: Limited(range)Timing accuracyGenerating theAccuracy: meterseasily achieve;source signal;Hardware: SourceCalibration of theSpeed in thegeneratorsensormediumUltrasonicAdd sonar capabilityNew SensorRange: Very limited(range)to nodes;Line-of-sight onlyAccuracy: sub-meterTiming accuracyLimited rangeHardware:easily achievedTransducers and LensInfraredExisting SensorLine-of-sight only;Range: Limited(range)Generating theAccuracy: meterssource signal;Hardware: SourceTiming accuracygenerator, High speedaccurate timingVisualCapture of targetComms bandwidth;Range: UnlimitedimageAutomatedAccuracy: 10'sprocessing;metersNode roof real-Hardware: Camera,estatefish-eye lensRadio (range)Existing assetTiming accuracyRange: GoodMeasurement rangeAccuracy: metersmatches commsHardware: Highrangespeed accurate timingRadioExisting assetAccuracy limited byRange: Limited(rangepropagation model;Accuracy: poorestimate fromHeavily affected byHardware: Existspowermultipathmeasurement)Radio (angle)Simplified arrayMultiple antennas;Range: Goodposition locationHeavily affected byAccuracy: Not GoodcalculationmultipathHardware: Multipleantennas, phasecomparators“Assisted”Minimal extraAssistance requiredRange: Goodhardware;Accuracy: GoodAccuracy largelyHardware: minimallimited by amountof assistance
For example, global satellite positioning (GPS) can be used to determine covert absolute positions. GPS can also provide an absolute timing reference. However, GPS receivers are not sensors and the accuracy measurements fall within the range of meters. An ultrasonic system provides improved accuracy measurements, but is effective over limited ranges. As the information in Table 1 shows, there is a need for a method and system that overcome the above limitations of conventional positioning technology.